What is the difference when a integer, string and array pass as function parameter in javascript

Question

As question, What is the difference when a integer, string and array pass as function parameter in javascript?

Below are my question:

<html>
    <head>
        <script>
            var a = 0;
            var b = new Array();
            b.push(0);

            function Add(num) {
                num++;
            }

            function Add1(num) {
                num[0]++;
            }

            Add(a);
            Add1(b);

            alert(a);
            alert(b[0]);
        </script>
    </head>

    <body></body>
</html>

And it ended up provide two different value, why? The first result 0 and the second one is 1

VisioN · Accepted Answer · 2014-04-22 13:39:46Z

3

Arrays as objects are passed in functions by reference while primitives (e.g. strings and numbers) are passed by value. Here is an example:

function test(arr, obj, prim) {
    arr[0]++;    // by reference
    obj.prop++;  // by reference
    prim++;      // by value

    return prim; // to get the amended primitive value back
}

var arr = [0],
    obj = { prop: 0 },
    prim = 0,
    result;

result = test(arr, obj, prim);

console.log(arr, obj, prim);  // [1], Object {prop: 1}, 0
console.log(result);          // 1

GOOD ARTICLE: http://snook.ca/archives/javascript/javascript_pass

edited Apr 22, 2014 at 13:39

answered Apr 22, 2014 at 13:34

VisioN

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2 Comments

dramasea Over a year ago

so the function will change the reference value? any extra information or reference so I can read on? Thanks

VisioN Over a year ago

@dramasea Strings and numbers are primitive types, arrays and objects are not. You may read a nice article about it in the updated answer.

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